Method for repairing defects in a metallic substrate using welding

ABSTRACT

A method for repairing defects in a metallic substrate comprising the steps of placing a consumable filler slug in contact with the substrate in the vicinity of the defect; bringing a first electrode and a second electrode in contact with the consumable slug and applying a pressure to the consumable slug; and transmitting electrical current between the electrodes for a period, thereby resistively heating the consumable slug and the metallic substrate resulting in coalescence in a substantially liquid pool that fills the defect. The pool is then cooled to solidification under the pressure of the electrodes. The electrodes are then removed from contact with the consumable slug and excess material may be removed. The consumable slug may be formed as a single unit or multiple sections, and may incorporate sacrificial retainers to add additional defect filling material, retain the pool, and seal the pool from atmosphere.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was not made as part of a federally sponsored research ordevelopment project.

TECHNICAL FIELD

The present invention relates to the field of material defect repair;particularly, to a method and apparatus for repairing material defectsutilizing a consumable filler slug, electrical current, and pressure toresistively melt the slug and repair the defect.

BACKGROUND OF THE INVENTION

Repairing defects in manufactured assemblies costs industries hundredsof millions of dollars each year. In fact, many industries viewrepairing defects in assemblies constructed of relatively thin metallicsheet materials, and the very high cost of these repairs, as a necessaryevil and have invested heavily in preventing such defects rather thanidentifying more cost effective ways to repair such defects. Theaircraft industry is just one of many industries plagued by thisproblem.

In the aircraft industry, parts are often manufactured to very exactingtolerances. As such, penetrations in aircraft parts are generally notmade until after the part is manufactured and meets the predeterminedtolerances. Such penetrations may be required for the insertion ofbolts, or rivets, or as a means for cooling the part. One can easilyappreciate that many of the hundreds of thousands of such penetrationsin an aircraft are misplaced during assembly despite even the mostexacting quality control measures. Such undesired holes, or materialdefects, then need to be repaired, while minimizing negative effects tothe part. Additionally, the need frequently arises to repair damaged,corroded, or worn holes in parts that have already been in service for aperiod of time.

The aircraft industry, as well as virtually all industries thatexperience similar problems, currently rely upon arc welding andfriction plug welding to repair such defects. Arc welding repair ofrelatively thin sheet metallic substrates requires a very skilledwelder. Additionally, no matter how skilled the welder, the very natureof arc welding results in a large amount of heat input that is appliedasymmetrically over the defect to repair the defect. As such, arcwelding repairs have large heat affected zones that can influencemechanical and corrosion performance in the repair area. The large heataffected zone often results in local distortion of the repairedsubstrate that then requires post-weld treatment to return the substrateto the desired tolerances. A further limitation to arc welding repairsis the significant amount of pre and post weld preparation of the defectarea required to produce a quality weld and ensure the desired partgeometry is produced.

An even greater limitation introduced when using arc welding to repairdefects is that the repair weld is often of less than optimal qualityand that filler materials must often be used that reduce performance ofthe component to improve the weldability of the surrounding substrate.This can result in repairs of significantly less strength than thesurrounding substrate. For instance, filler metals having very highductility, but less than desired strength and corrosion properties, areoften required to minimize solidification cracking when using arcwelding to repair defects in materials that have been in use for aperiod of time and suffer from reduced ductility. This is particularlytrue in the aircraft industry where holes often require repair after theaircraft has been in service for several years. In such repairs it isnot uncommon that filler metals having strengths of 60% of the strengthof the adjoining parent material are required so as to avoidsolidification cracking of the weld repair.

As previously mentioned, friction plug welding has also been used torepair defects and holes in manufactured assemblies. Friction plugwelding offers some advantages over the previously mentioned arc weldingmethod in that it is a solid state process, and produces a narrow heataffected zone. This minimizes the influence on mechanical and corrosionproperties of the finished product.

The friction plug welding process has some definite limitations, whichare primarily associated with the need to apply and react the mechanicalloads associated with this process. Friction welding uses a consumableplug that must be rotated at high rpm and then pressed into a taperedhole to produce the repair. As such, the consumable plug is generallymuch larger than needed to produce the repair so that the plug can berigidly gripped to allow the transfer of high speed and large loads. Thereaction of the loads induced into the component by the plug typicallyrequires specialized rigid tooling. The friction welding equipment usedto produce the weld is typically very large due to the rotational energythat must be applied to the plug and the axial load necessary to forcethe plug into the tapered hole. An additional limitation of frictionplug welding is that it requires line of sight access to the repairarea, thereby limiting it to only the most simple repairs. Further,friction plug welding equipment is expensive and less readily availablethan arc welding or resistance welding equipment.

The instant invention addresses many of the shortcomings of the priorart and allows for previously unavailable benefits. A method ofrepairing defects in a metallic substrate that overcomes many of thelimitations of the prior art has long been needed. The method of thepresent invention is designed to reduce the need for a skilled welder toeffect repairs, and to result in a repaired substrate having greatlyimproved material properties, while negating many of the limitations ofprior repair techniques. The method accomplishes such improvements byutilizing a relatively low heat input applied over a very short periodof time and cooling of the repaired substrate. Additional benefits ofthe present method arise from the substantially uniform application ofheat to the repair region and the fact that it typically requires nospecial preparation of defects prior to repair. Further, the equipmentused to produce the repair is common in many manufacturing facilitiesand is relatively inexpensive to procure and maintain.

SUMMARY OF INVENTION

In its most general configuration, the present invention advances thestate of the art with a variety of new capabilities and overcomes manyof the shortcomings of prior methods in new and novel ways. In one ofthe many preferable configurations, the method comprises a method ofrepairing defects in a metal substrate using welding. The methodcomprises, in general, the steps of placing a consumable filler slug incontact with the substrate in the vicinity of the defect; bringing afirst electrode and a second electrode in contact with the consumablefiller slug and applying a pressure to the consumable filler slug; andtransmitting electrical current between the electrodes through the slugfor a period of time. This resistively heats the slug and the metallicsubstrate resulting in coalescence in a substantially liquid pool thatfills the defect; followed by cooling the substantially liquid pool tosolidification under the pressure of the first electrode and the secondelectrode; and removing the electrodes from contact with the consumablefiller slug.

The metallic substrate of the present invention may be formed of anyresistance spot weldable metallic substance, but has particularadvantages in repairing titanium alloys, high strength austeniticnickel-chromium-iron alloys and superalloys, and aluminum. Substratesmay be a single sheet of material having a first surface and a secondsurface, but this method may perform equally as well on substrateshaving complex curvature, variable thickness, and heterogeneouscompositions.

The present method may repair defects having a wide variety ofcharacteristics, such as tears, voids extending all the way through thesubstrate, dents, or areas of compression or reduced thickness. Themethod generally begins with the placement of the consumable filler slugin contact with the substrate in the vicinity of the defect. Theconsumable filler slug may be formed in a number of equally effectiveconfigurations, such as single units or multiple sections, or conformingor merely roughly approximating the defect. The slug may also take theform of a washer or other configuration that works preferably with theelectrodes or achieves desired flow to, or within, the defect.

An embodiment having multiple slug sections is contemplated. In such anembodiment, the consumable filler slug includes a first slug section anda second slug section such that the slug sections are configured to bein contact through the void. The consumable filler slug may be used inconjunction with at least one sacrificial retainer. The sacrificialretainer may be placed on each open end of the void, however, thepresent method is equally effective utilizing a single sacrificialretainer. A multi-part slug may incorporate exterior retaining lips thatact in many ways as a sacrificial retainer.

The consumable filler slug and sacrificial retainer may be formulated tohave properties similar, or dissimilar, to the metallic substrate, or bemade of the same material as the metallic substrate. This can lead tothe repaired area having substantially the same, or markedly different,properties from that of the substrate. For example, the presentinvention's ability to use consumable filler slugs of virtually anyresistance weldable composition creates the ability to augment thestrength or corrosion performance of the metallic substrate.

The next step in the method includes bringing the electrodes in contactwith the consumable filler slug and applying a pressure to the slug.Then, with the electrodes in contact with the slug, and potentially withthe metallic substrate, an electrical current is transmitted from thefirst electrode to the second electrode through the slug for a period oftime thereby resistively heating the slug and the metallic substrate.The heat generated from the current flow and the resistance of the slugand metallic substrate results in the melting of a substantial portionof the slug and a portion of the metallic substrate and coalescence intoa substantially liquid pool that fills the defect. The first and secondelectrodes exert a pressure on the substantially liquid pool as it iscreated and as it solidifies.

Unlike other repair techniques, the consumable filler slug and metallicsubstrate material surrounding the resistively heated area preventoxidation. Therefore, this method does not require the use of ashielding gas, thereby reducing the cost of repairing defects as wellincreasing the versatility of the method. Additionally, theincorporation of a sacrificial retainer creates the ability to furtherseal the substantially liquid pool from the surrounding atmosphere, ifdesired. Further, the sacrificial retainer tends to keep the electrodesclean. In such an embodiment, the sacrificial retainer is placed betweenthe slug and the first electrode through which the current passes andresistively heats. A portion of the sacrificial retainer coalesces intothe pool and a portion of the sacrificial retainer remains solid andconstrains the flow of the pool and seals the pool from the surroundingatmosphere. The portion of the sacrificial retainer that remains solid,and any portion of the solidified pool, may be removed by finishingprocesses to bring the level of the repaired defect down to the level ofthe adjoining metallic substrate. The method may be performed such thatthe electrical current is substantially uniformly transmitted from thefirst electrode to the second electrode. Such uniform transmissionresults in substantially symmetric resistive heating of the slug and themetallic substrate and substantially uniform heating of the defect,unlike previous defect repair techniques having non-symmetric thermalprofiles around the defect during repair and solidification. Theapplication of nearly uniform heat around the entire perimeter of thedefect substantially helps eliminate distortion.

With the instant invention, the period of the heat input and the amountof heat input of the present invention is significantly less than thatof previous defect repair techniques. Further, the amount of heat thatremains in the repaired metallic substrate is significantly less usingthe method of the present invention, as will be discussed later herein,further reducing distortion and improving performance of the repaireddefect.

The substantially liquid pool is then cooled to solidification. Thepressure exerted on the substantially liquid pool during solidificationreduces contraction stresses during solidification of the pool since thefusion zone remains under compressive loading. This tends to preventsolidification and liquation cracks from forming in the repaired defect.The cooling of the liquid pool is generally accomplished by utilizingwater cooled electrodes, but may be accomplished through the use of anumber of heat transfer processes. The cooling of the pool, as well asthe short period of heat input, produces a repaired metallic substratecontaining very little residual heat. The small amount of residual heatin the repaired metallic substrate and rapid cooling of thesubstantially liquid pool further minimize distortion and significantlyimprove the performance of the repaired defect.

After obtaining the desired predetermined level of cooling, theelectrodes are removed from contact with the slug and the repair iscomplete. Alternative embodiments may include providing local post weldheat treatment after producing the repair, but before releasing thewelding pressure. Such post weld heat treatment may resistively heat therepair for a predetermined time to locally produce a predeterminedmicrostructure. Additional embodiments may include additional steps suchas a step of removing excess slug material so that the surface of therepaired defect is substantially consistent with the level of theadjoining substrate surface.

Variations, modifications, alternatives, and alterations of the variouspreferred embodiments, processes, and methods may be used alone or incombination with one another as will become more readily apparent tothose with skill in the art with reference to the following detaileddescription of the preferred embodiments and the accompanying figuresand drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Without limiting the scope of the present invention as claimed below andreferring now to the drawings and figures:

FIG. 1 shows a metallic substrate having various defect embodiments inelevated perspective view, not to scale;

FIG. 2 shows a partial cross-sectional view of the metallic substratehaving a cylindrical void, not to scale;

FIG. 3 shows a partial cross-sectional view of the metallic substratehaving a cylindrical void with a consumable filler slug in place, not toscale;

FIG. 4 shows a partial cross-sectional view of the setup of FIG. 3 withthe electrodes in place, not to scale;

FIG. 5 shows a partial cross-sectional view of the setup of FIG. 4having a substantially liquid pool, not to scale;

FIG. 6 shows a partial cross-sectional view of the setup of FIG. 5 withthe electrodes removing heat from the pool and metallic substrate, notto scale;

FIG. 7 shows an embodiment incorporating a plurality of sacrificialretainers in partial cross-sectional view, with the electrodes in place,not to scale;

FIG. 8 shows a partial cross-sectional view of the setup of FIG. 7having a substantially liquid pool, not to scale;

FIG. 9 shows an alternative defect containing a consumable filler slugin partial cross-sectional view, not to scale;

FIG. 10 shows an alternative embodiment of the consumable filler slughaving a first slug section and a second slug section, in partialcross-sectional view, not to scale;

FIG. 11 shows an alternative embodiment of the consumable filler slughaving a first slug section and a second slug section, in partialcross-sectional view, not to scale;

FIG. 12 shows a repaired defect after removal of the excess consumablefiller slug, in partial cross-sectional view, not to scale; and

FIG. 13 shows a repaired defect having the repaired surface brought tothe level of the surrounding surfaces, in partial cross-sectional view,not to scale.

DETAILED DESCRIPTION OF THE INVENTION

The method for repairing a defect in a metallic substrate using weldingenables a significant advance in the state of the art. The preferredembodiments of the apparatus accomplish this by new and novel methodsthat are configured in unique and novel ways and which demonstratepreviously unavailable but preferred and desirable capabilities. Thedescription set forth below in connection with the drawings is intendedmerely as a description of the presently preferred embodiments of theinvention, and is not intended to represent the only form in which thepresent invention may be constructed or utilized. The description setsforth the designs, functions, means, and methods of implementing theinvention in connection with the illustrated embodiments. It is to beunderstood, however, that the same or equivalent functions and featuresmay be accomplished by different embodiments that are also intended tobe encompassed within the spirit and scope of the invention.

One exemplary embodiment of the method for repairing a defect 200 in ametallic substrate 100 using welding includes the steps of placing aconsumable filler slug 300 in contact with the substrate 100 in thevicinity of the defect 200; bringing a first electrode 410 and a secondelectrode 420 in contact with the consumable filler slug 300 andapplying a pressure to the consumable filler slug 300; transmittingelectrical current 440 from the first electrode 410 to the secondelectrode 420 through the consumable filler slug 300 for a period oftime thereby resistively heating the consumable filler slug 300 and themetallic substrate 100 resulting in coalescence in a substantiallyliquid pool 500 that fills the defect 200; cooling the substantiallyliquid pool 500 to solidification under the pressure of the firstelectrode 410 and the second electrode 420; and removing the firstelectrode 410 and the second electrode 420 from contact with theconsumable filler slug 300.

The metallic substrate 100 of the present invention may be formed of anyresistance spot weldable metallic substance. The method has particularadvantages in repairing titanium alloys, high strength austeniticnickel-chromium-iron alloys and superalloys, and aluminum, but may beused with virtually any metal that can be resistively melted.Additionally, the substrate 100 may be configured in any number of waysthat facilitate the transfer of current 440 through the defect 200. Thesubstrate 100 is illustrated in FIG. 1 through FIG. 13 as a single sheetof material having a first surface 110 and a second surface 120. Onewith skill in the art will appreciate that this is just one illustrativeembodiment and that this method may perform equally as well onsubstrates 100 of varied geometries including, but not limited too,substrates 100 having complex curvature, variable thickness, andheterogeneous compositions. Further, one with skill in the art willrecognize that the shape of the weld pool 500 in FIG. 5, FIG. 6, andFIG. 8 is merely schematic in nature and does not represent the actualshape of the weld pool in practice.

The present method may repair defects 200 having a wide variety ofcharacteristics. For instance, the method may be used to repair defects200 that consist of a tear in the substrate 100, those that are voids210 extending all the way through the substrate 100, dents, or areas ofcompression or areas of reduced thickness, in the substrate 100, as seenin FIG. 1, and any number of surface imperfections such as corrodedholes, mislocated holes, oversized holes, and holes that are out ofround. The method is described herein generally with reference to adefect 200 that is a void 210 extending through the substrate 100 fromthe first surface 110 to the second surface 120, as illustrated in FIG.2, but the method applies equally to the number of other defects 200referred to herein.

The method generally begins with the placement of the consumable fillerslug 300 in contact with the substrate 100 in the vicinity of the defect200. The consumable filler slug 300 may be formed in a number of equallyeffective configurations. For instance as illustrated in FIG. 3, theconsumable filler slug 300 may be a single unit or may be composed ofmultiple slug sections, as seen in FIG. 10. The consumable filler slug300 may, but is not required to, substantially conform to the shape andconfiguration of the defect 200. For instance, FIG. 9 illustrates anembodiment having a consumable filler slug 300 that substantiallyconforms to the shape of the dent, or defect 200. The consumable fillerslug 300 of the present embodiment may be formed in any number ofalternative shapes. For instance, the filler slug 300 may take the formof a washer or other configuration that works preferably with theelectrodes or achieves desired flow to, or within, the defect 200.

Similarly, the consumable filler slug 300 may be configured tosubstantially conform to the void 210 extending through the substrate100, as illustrated in FIG. 3. The void 210 of this particularembodiment is substantially cylindrical in shape having a diameter 220and a length equal to the thickness 130 of the substrate 100, as seen inFIG. 2. However, in practice it is common for the void to have a lengththat is less than the substrate 100 when necking of the material hasoccurred. This particular embodiment will be referred to throughout forease of explanation and illustration. Referring again to FIG. 3, anembodiment of the consumable filler slug 300 for such a void 210 is onebeing substantially cylindrical in shape, having a diameter 340, and adistal end 310 and a proximal end 320 separated by a length 330.Typically, the diameter of the consumable filler slug 300 is less thanthe diameter of the void 210 for ease of installation, but this is notrequired and a consumable filler slug 300 that necessitates being driveninto the defect 200 is anticipated.

An embodiment having multiple slug sections is illustrated in FIG. 10.In this embodiment the consumable filler slug 300 includes a first slugsection 350 and a second slug section 360 such that the first slugsection 350 and the second slug section 360 are configured to be incontact through the void 210. In this particular embodiment the firstslug section 350 and the second slug section 360 incorporate retaininglips 352,362 to provide the same advantages as the sacrificial retainers370, discussed later herein. Further, retaining lips 352, 362 of FIG. 10may be formed with upturned edges, as seen in FIG. 11. The upturnedretaining lips 352,362 of FIG. 11 may be configured to cooperate withthe shape of the first or second electrodes 410, 420. The configurationof FIG. 11 promotes accurate alignment and placement of the consumablefiller slugs 350, 360 and the electrodes 410, 420, and may reduce, oreliminate, the need for non-electrically conductive locating fixtures.

The consumable filler slug 300 may be used in conjunction with at leastone sacrificial retainer 370, as seen in FIG. 7. The embodimentsillustrated in FIG. 7 and FIG. 8 utilize a sacrificial retainer 370 oneach open end of the void 210, however the present method is equallyeffective utilizing a single sacrificial retainer 370. In a furtherembodiment the beneficial features of the sacrificial retainer 370 maybe incorporated directly into the consumable filler slug 300, as will beexplained later herein.

The consumable filler slug 300 and the sacrificial retainer 370 may beformulated to have properties similar, or dissimilar, to the metallicsubstrate 100. In fact, the consumable filler slug 300 and thesacrificial retainer 370 may be the same material as the metallicsubstrate 100. This is particularly beneficial in that the repaireddefect 700 is no longer limited by the use of a limited number of fillerproducts, as is the case with GTAW welding.

For example, it is widely understood that grain size plays a notablerole in both notched and smooth fatigue tests of many titanium alloys.Generally, GTAW repairs of titanium sheet metal result in grains havinga diameter between approximately one-half of the metal thickness to theentire thickness, thereby greatly reducing the performance of therepair. The method of the present invention may be used to produce finegrained structure in the repaired defect and a minimal heat affectedzone. In fact, the present method may be used to achieve grain size inthe repaired defect that is close to that of the base metal. Such grainsize control may be used to greatly enhance the performance of therepaired defect, especially in fatigue. For example, the changes infatigue strength of TI-6Al-4V at 10⁷ cycles to failure may vary between406 MPa and 551 MPa, depending on grain size. This method may be used tocontrol grain size such that the best performance grain size for eachalloy may be achieved in the repaired defect.

In yet another example, GTAW welds are generally used to repair defects200 in 6061 aluminum. In this situation a 4043 aluminum filler is used.The deposited weld metal in the defect 200, a misplaced rivet hole inthis example, generally has a yield strength of 10,500 psi and anultimate strength of 21,000 psi. The present method may use a consumablefiller slug 300 of 6061 aluminum, which after repair and heat treatmentcan achieve a yield strength of 39,000 psi and an ultimate strength of45,000 psi, an improvement of almost a factor of 4 for the yieldstrength and more than doubling the ultimate strength.

A further example of the benefits of this invention is illustrated innickel-based and cobalt alloys that have been in service and requirerepair of a defect 200. Repairing the defect 200 in such a materialgenerally requires the use of a filler metal having high ductilitybecause the elongation of the base material is often greatly reducedduring its life which tends to promote solidification cracking ofrepairs. For instance the strength of an overaged high strengthaustenitic nickel-chromium-iron alloy part can be approximately 180,000psi, but the part will generally have very low ductility. Therefore,repairing a defect 200 in such a material may require the use of a lowerstrength alloy having high ductility to reduce the likelihood ofcracking, but a strength of only 100,000 psi. Such ductility problemsare eliminated by the present invention, in part due to the fact thatthe substantially liquid pool 500 is kept under constant compressiveloading, as will be discussed later herein.

Still further, the present inventions ability to use consumable fillerslugs 300 of virtually any composition creates the ability to augmentthe strength of the metallic substrate 100. This ability is desired in anumber of industries. For instance, in many industries the thickness ofsheet metal parts is determined by the allowable stress at a particularload connection point, such as a rivet or bolt hole. If the strength ofthe material could be locally augmented in the vicinity of the rivet orbolt hole, then the thickness of the remainder of the part may bereduced. In high temperature applications, such as the combustor of ajet engine, it would be advantageous to place a material with bettercorrosion and oxidation resistance at higher temperatures in only thoseareas subjected to particularly high loading, while constructing thebulk of the combustor from less expensive materials. As such, thepresent method may be used to create engineered surfaces designed toaccept the higher temperatures in particular areas. This may beaccomplished by using the method of the present invention to essentiallyline a bolt or rivet hole in one substrate with a material having bettercorrosion or oxidation resistance characteristics.

The next step in the method includes bringing a first electrode 410 anda second electrode 420 in contact with the consumable filler slug 300and applying a pressure, or force 430, to the consumable filler slug300, as seen in FIG. 4. Then, with the electrodes in contact with theconsumable filler slug 300, and potentially with the metallic substrate100, an electrical current 440 is transmitted from the first electrode410 to the second electrode 420 through the consumable filler slug 300for a period of time, thereby resistively heating the consumable fillerslug 300 and the metallic substrate 100. The heat generated from thecurrent 440 transfer and the resistance of the consumable filler slug300 and metallic substrate 100 results in the melting of a substantialportion of the consumable filler slug 300 and a portion of the metallicsubstrate 100, resulting in coalescence into a substantially liquid pool500 that fills the defect 200, illustrated in FIG. 5. The first andsecond electrodes 410,420 exert a pressure on the substantially liquidpool 500 as it is created and as it solidifies.

Unlike other repair techniques, the thermal cycle of the present methodis so rapid that oxidation is not an issue. As such, this method doesnot require the use of a shielding gas thereby reducing the cost ofrepairing defects 200 as well as increasing the versatility of themethod. Additionally, the incorporation of the sacrificial retainer 370,seen in FIG. 7, creates the ability to quickly seal the substantiallyliquid pool 500 from the surrounding atmosphere, if desired. Further,the sacrificial retainer 370 helps minimize tip sticking and pickup onthe welding electrode thereby lengthening the electrode tip life. Forinstance, the substantially liquid pool 500 illustrated in FIG. 8 issealed from the surrounding atmosphere by the sacrificial retainers 370in approximately 1/100 second. In such an embodiment the sacrificialretainer 370 is placed between the consumable filler slug 300 and thefirst electrode 410 through which the current 440 passes and resistivelyheats. A portion of the sacrificial retainer 370 coalesces into the pool500 and a portion of the sacrificial retainer 370 remains solid andconstrains the flow of the pool 500 and seals the pool 500 from thesurrounding atmosphere. The portion of the sacrificial retainer 370 thatremains solid, and any portion of the solidified pool, may be removed byfinishing processes to bring the level of the repaired defect down tothe level of the adjoining metallic substrate 100, as seen in FIG. 13.It is estimated that the repair time required to correct defectscommonly encountered in the manufacture of a jet engine augmentor ductwill be reduced from 10 hours, when using traditional arc weldingmethods, to 3 hours, when using the present method.

In yet another embodiment the method is performed such that theelectrical current 440 is substantially uniformly transmitted from thefirst electrode 410 to the second electrode 420. Such uniformtransmission results in substantially symmetric resistive heating of theconsumable filler slug 300 and the metallic substrate 100 andsubstantially uniform heating of the defect 200, unlike previous defect200 repair techniques having non-symmetric thermal profiles around thedefect 200 during repair and solidification. The application of nearlyuniform heat around the entire perimeter of the defect 200 substantiallyeliminates distortion. For example, identical one-inch by three-inchsamples of 0.040 inch thick Ti 6-4 with identical defects were repairedusing GTAW welding and the method of the present invention. The GTAWwelded sample resulted in a distortion of 0.070 inches out of the plane.The sample repaired using the method of the present invention resultedin a distortion of 0.003 inches out of the plane, over a 95% reductionin distortion. Repairs made using GTAW welds generally require extensiverework to return the repaired metallic substrate 100 to the originaltolerances. The sample using the present method was repaired using class2 copper 1/2 inch body diameter electrodes having a face diameter of5/16 inch and producing approximately 6 volts, 8000 amps, for ⅙ second.

Additionally, the period of the heat input and the amount of heat inputof the present invention is significantly less than that of previousdefect repair techniques. For example, the present method may utilize aheat input of roughly 8,000 joules to repair most defects, whereascommonly used GTAW weld repair produces approximately 23,400 joules ofheat input, almost four times that of the present invention. Further,the amount of heat that remains in the repaired metallic substrate 100is significantly less using the method of the present invention, as willbe discussed later herein, further reducing distortion and improvingperformance of the repaired defect 700.

The substantially liquid pool 500 is then cooled to solidification. Thepressure exerted on the substantially liquid pool 500, duringsolidification ensures that tensile stress is reduced duringsolidification of the pool 500 since the fusion zone remains undercompressive loading. This tends to prevent solidification cracks fromforming in the repaired defect 700. The cooling of the liquid pool 500is generally accomplished by utilizing water cooled electrodes for thefirst and second electrode 410, 420, but may be accomplished through theuse of a number of heat transfer processes, as illustrated by the heattransfer flow arrows 600 in FIG. 6 and FIG. 8. The cooling of the pool500, as well as the short period of heat input, produces a repairedmetallic substrate 100 containing very little residual heat. Forexample, the previously discussed sample produced using this method hadapproximately 240 joules of residual heat almost immediately after beingsubjected to 8,000 joules. Conversely, the sample repaired using GTAWwelding had roughly one hundred percent of the input 23,400 joulesremaining in the substrate 100 upon completion of the repair. Oneembodiment of the present method is specifically directed to producing arepaired metallic substrate 100 having less than approximately 5% of theheat input actually remaining in the repaired metallic substrate 100upon completion of the repair.

The small amount of residual heat in the repaired metallic substrate 100and rapid cooling of the substantially liquid pool 500 further minimizedistortion and significantly improves the performance of the repaireddefect 700. For instance, the rapid cooling of the liquid pool 500 underpressure can significantly reduce the grain size in the resultingrepaired metallic substrate 100. These benefits are particularlybeneficial in the repair of titanium because the process greatlyreduces, or eliminates, the formation of alpha case in the titanium,which is highly undesirable in fatigue sensitive applications. In yetanother embodiment of this invention, the amount of cooling applied tothe pool 500 is varied as the pool 500 solidifies to achieve a desiredpredetermined property. For instance, the varied cooling may be tuned toobtain a preferred grain size in the repaired metallic substrate 100.Additionally, the cooling rate may be set for a preferred cooling rateof the material of the metallic substrate 100.

After obtaining the desired predetermined level of cooling, the firstelectrode 410 and the second electrode 420 are removed from contact withthe consumable filler slug 300 and the repair is complete, as seen inFIG. 12. Alternative embodiments may include additional steps such as astep of removing excess consumable filler slug 300 material with amaterial processing device 800, such as a grinder, so that the surfaceof the repaired defect 700 is substantially consistent with the level ofthe adjoining substrate 100 surface, illustrated in FIG. 13. Removal ofexcess consumable filler slug 300 material is often desired as it mayserve as an indicator that the entire defect 200 has been repaired.

Numerous alterations, modifications, and variations of the preferredembodiments disclosed herein will be apparent to those skilled in theart and they are all anticipated and contemplated to be within thespirit and scope of the instant invention. For example, althoughspecific embodiments have been described in detail, those with skill inthe art will understand that the preceding embodiments and variationscan be modified to incorporate various types of substitute and oradditional or alternative materials, relative arrangement of elements,and dimensional configurations. Accordingly, even though only fewvariations of the present invention are described herein, it is to beunderstood that the practice of such additional modifications andvariations and the equivalents thereof, are within the spirit and scopeof the invention as defined in the following claims. The correspondingstructures, materials, acts, and equivalents of all means or step plusfunction elements in the claims below are intended to include anystructure, material, or acts for performing the functions in combinationwith other claimed elements as specifically claimed.

1. A method for repairing a defect in a metallic substrate usingwelding, the substrate having a first surface and a second surface, themethod comprising: a) placing a consumable filler slug in contact withthe substrate in the vicinity of the defect; b) transmitting electricalcurrent from a first electrode to a second electrode in the vicinity ofthe defect for a period, thereby resistively heating the consumablefiller slug and the metallic substrate resulting in coalescence in asubstantially liquid pool that substantially fills the defect, the firstelectrode and the second electrode applying pressure to thesubstantially liquid pool; c) cooling the substantially liquid pool tosolidification under the pressure of the first electrode and the secondelectrode producing a repaired metallic substrate; and d) removing thefirst electrode and the second electrode from contact with the repairedmetallic substrate.
 2. The method of claim 1, further including the stepof applying a sacrificial retainer between the consumable filler slugand the first electrode through which the current passes and resistivelyheats, a portion of the sacrificial retainer coalescing into the pooland a portion of the retainer remaining solid and constraining the flowof the pool and sealing the pool from the surrounding atmosphere.
 3. Themethod of claim 1, wherein the defect is a void extending from thesubstrate first surface to the substrate second surface.
 4. The methodof claim 3, wherein the consumable filler slug includes a first slugsection and a second slug section, the first slug section having aretaining lip configured to be in contact with the substrate firstsurface and the second slug section having a retaining lip configured tobe in contact with the substrate second surface such that as currentpasses from the first electrode to the second electrode and resistivelyheats the first slug section and the second slug section a portion ofeach retaining lip coalesces into the pool and a portion of eachretaining lip remains solid to constrain the flow of the pool.
 5. Themethod of claim 1, further including the step of applying a firstsacrificial retainer between the consumable filler slug and the firstelectrode and applying a second sacrificial retainer between theconsumable filler slug and the second electrode, wherein the void issubstantially cylindrical in shape, having a diameter and a volume, andthe consumable filler slug is substantially cylindrical having adiameter smaller than the diameter of the void, a volume, and a distalend and a proximal end whereby the consumable filler slug is configuredto be received by the void, such that current passes and resistivelyheats the sacrificial retainers and the consumable filler slug and aportion of the sacrificial retainers coalesce into the pool and aportion of the retainers remain solid and constrain the flow of the pooland seal the pool from the surrounding atmosphere.
 6. The method ofclaim 1, wherein the electrical current is substantially uniformlytransmitted from the first electrode to the second electrode therebysubstantially symmetrically resistively heating the consumable fillerslug and the metallic substrate and substantially uniformly heating thedefect.
 7. The method of claim 1, wherein the period of transmittingelectrical current from the first electrode to the second electrode isless than approximately 200 milliseconds.
 8. The method of claim 1,wherein less than approximately 5% of the heat input to the consumablefiller slug and the metallic substrate by the transmission of currentfrom the first electrode to the second electrode remains in the repairedmetallic substrate upon removal of the first electrode and the secondelectrode.
 9. The method of claim 1, wherein the amount of coolingapplied to the pool is varied as the pool solidifies to achieve adesired predetermined property.
 10. The method of claim 9, wherein thedesired predetermined property is a preferred grain size.
 11. The methodof claim 1, wherein the consumable filler slug is composed of the samematerial as the substrate.
 12. The method of claim 1, wherein therepaired metallic substrate is substantially free of distortion.
 13. Themethod of claim 1, wherein the repaired metallic substrate issubstantially free of solidification cracks.
 14. The method of claim 1,further including a step of removing excess consumable filler slugmaterial, after the electrodes are removed, so that the surface of therepaired defect is substantially consistent with the level of theadjoining substrate surface.
 15. A method for repairing a defect in ametallic substrate using welding, the substrate having a first surfaceand a second surface, the method comprising: a) placing a consumablefiller slug in contact with the substrate in the vicinity of the defect;b) transmitting electrical current substantially uniformly from a firstelectrode to a second electrode in the vicinity of the defect for aperiod, thereby substantially symmetrically resistively heating theconsumable filler slug and the metallic substrate resulting incoalescence in a substantially liquid pool that substantially fills thedefect, the first electrode and the second electrode applying pressureto the substantially liquid pool; c) cooling the substantially liquidpool to solidification under the pressure of the first electrode and thesecond electrode producing a repaired metallic substrate; d) removingthe first electrode and the second electrode from contact with therepaired metallic substrate; and e) removing excess consumable fillerslug material so that the surface of the repaired defect issubstantially consistent with the level of the adjoining substratesurface.
 16. The method of claim 15, further including the step ofapplying a sacrificial retainer between the consumable filler slug andthe first electrode through which the current passes and resistivelyheats, a portion of the sacrificial retainer coalescing into the pooland a portion of the retainer remaining solid and constraining the flowof the pool and sealing the pool from the surrounding atmosphere. 17.The method of claim 15, wherein the defect is a void extending from thesubstrate first surface to the substrate second surface.
 18. The methodof claim 17, wherein the consumable filler slug includes a first slugsection and a second slug section, the first slug section having aretaining lip configured to be in contact with the substrate firstsurface and the second slug section having a retaining lip configured tobe in contact with the substrate second surface such that as currentpasses from the first electrode to the second electrode and resistivelyheats the first slug section and the second slug section a portion ofeach retaining lip coalesces into the pool and a portion of eachretaining lip remains solid to constrain the flow of the pool.
 19. Themethod of claim 15, further including the step of applying a firstsacrificial retainer between the consumable filler slug and the firstelectrode and applying a second sacrificial retainer between theconsumable filler slug and the second electrode, wherein the void issubstantially cylindrical in shape, having a diameter and a volume, andthe consumable filler slug is substantially cylindrical having adiameter smaller than the diameter of the void, a volume, and a distalend and a proximal end whereby the consumable filler slug is configuredto be received by the void, such that current passes and resistivelyheats the sacrificial retainers and the consumable filler slug and aportion of the sacrificial retainers coalesce into the pool and aportion of the retainers remain solid and constrain the flow of the pooland seal the pool from the surrounding atmosphere.
 20. The method ofclaim 15, wherein less than approximately 5% of the heat input to theconsumable filler slug and the metallic substrate by the transmission ofcurrent from the first electrode to the second electrode remains in therepaired metallic substrate upon removal of the first electrode and thesecond electrode.
 21. A method for repairing a defect that is asubstantially cylindrically shaped void in a metallic substrate usingwelding, the substrate having a first surface and a second surface, andthe void extending from the first surface to the second surface, themethod comprising: a) placing a substantially cylindrical consumablefiller slug in the void and applying a first sacrificial retainer on thefirst surface and a second sacrificial retainer on the second surfacesuch that the first sacrificial retainer and the second sacrificialretainer cover the void and the consumable filler slug; b) transmittingelectrical current substantially uniformly from a first electrode to asecond electrode in the vicinity of the void for a period of less thanapproximately 200 milliseconds while applying pressure to the firstsacrificial retainer and the second sacrificial retainer, therebysubstantially symmetrically resistively heating the first sacrificialretainer, the consumable filler slug, the metallic substrate, and thesecond sacrificial retainer resulting in coalescence of a portion of thefirst sacrificial retainer, the consumable filler slug, a portion of thesubstrate, and a portion of the second sacrificial retainer in asubstantially liquid pool that substantially fills the void while beingretained by the first sacrificial retainer and the second sacrificialretainer; c) cooling the substantially liquid pool to solidificationunder the pressure of the first electrode and the second electrodeproducing a repaired metallic substrate such that less thanapproximately 5% of the heat input to the consumable filler slug and themetallic substrate by the transmission of the current remains in therepaired metallic substrate and the repaired metallic substrate issubstantially free of distortion; d) removing the first electrode andthe second electrode from contact with the first sacrificial retainerand the second sacrificial retainer; and e) removing excess consumablefiller slug material so that the surface of the repaired defect issubstantially consistent with the level of the adjoining substratesurface.